Knowledge of the location of a vehicle relative to its environment is crucial, particularly for autonomous vehicles. Presently there are a number of distinct systems which utilize internal or external reference systems to estimate position.
Internal reference is typically provided by inertial reference utilizing a gyroscope. Accurate gyroscopes, particularly digitally readable ones, are quite expensive and are relatively delicate.
Internal reference can also be provided by dead reckoning. Encoders on the drive system record the distance travelled by the wheels or tracks of the vehicle. This technique, also known as odometry, further includes steering encoders to record changes in orientation.
Other systems model the surrounding environment by reducing the environment to geometric features. The vehicle matches the perceived geometric model with the expected model and correlates them to determine its offset in position. The environment is typically modelled as a series of line segments representing surface features, or as a grid representing the probability of presence or absence of objects within particular locations.
Yet other systems rely on a number of markers placed in the environment. A landmark system utilizes markers placed along a path to denote the distance travelled.
Some systems calibrate positions at predetermined locations, or nodes, where a number of markers are installed to permit triangulation. One system uses three infrared beacons to triangulate position. Triangulation can also be accomplished using other forms of energy such as radio waves.
Another system triangulates its position using a rotating laser. The laser beam reflects off corner reflectors at designated locations. The system determines the angles among the reflectors to triangulate its position.